This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The localization of dopamine D1 and D2 receptors is highly controversial. Some laboratories have reported that 100% of striatal neurons co-express the two receptors while others have reported that only a fraction of them does (from 5 to 20%. Our goal is to determine if both receptors co-localize in adult as well as in embryonal neurons. For this, we have generated in our lab knockin mice that express dopamine D1R tagged with ECFP and dopamine D2R tagged with EYFP. These mice will be used to visualize the localization of endogenous receptors under normal conditions and after treatment with drugs of abuse. Furthermore, we have mated D1R-ECFP with D2R-EYFP mice to be able to perform FRET studies that will tell us if these two receptors might interact in vivo.